CSS Calc returning 0 but works in my fiddle

On my local machine using this and then inspecting the element it displays:

width: calc(0%);

When I put it in a fiddle it seems to be working.

The part that is working is the blue content div being the proper width to be next to the sidebar where as on my local the content div have 0% width. It shows the content in the div but not the background colour blue.